Summary form only given. This paper presents a new approach to security coordinated maintenance scheduling in deregulation wherein the independent system operator (ISO) does not generate a maintenance schedule by itself, but calls for maintenance scheduling plans from individual Gencos. The maintenance scheduling plans, when incorporated in a medium-term security constrained production scheduling program can result in unserved energy at one or more buses. Based on the information on bus-wise unserved energy, the ISO generates corrective signals for the Genco(s), and directs them to alter their maintenance plans in specific periods and re-submit. The proposed scheme exploits the concept of commons and domains to derive a novel factor to allocate the unserved energy at a bus to a set of generators responsible. Iterations between the Gencos and ISO continue until the coordination program has converged, and there is no unserved energy at any period in the system. A case-study for a large-scale power system, which is a representative reduction of the Ontario power system, is presented in the paper with insight on the coordination process. The proposed scheme is computationally simple, efficient and can be applied to real-sized power systems.